https://repositorio.ufu.br/handle/123456789/5149 Sun, 02 Aug 2026 03:07:28 GMT 2026-08-02T03:07:28Z https://repositorio.ufu.br/handle/123456789/49008 Title: Filmes finos baseados em hexacianoferratos de ferro e bismuto e nanomateriais de carbono para aplicação em dispositivos de armazenamento de energia Abstract: The objective of this work was the development and characterization of nanocomposite thin films based on iron (HCFFe) and bismuth (HCFBi) hexacyanoferrates combined with carbon nanomaterials (carbon nanotubes and reduced graphene oxide) for application in aqueous rechargeable batteries. The motivation of this study stems from the growing demand for efficient, safe, and low-cost energy storage technologies, such as aqueous electrolyte rechargeable batteries, which emerge as promising alternatives to lithium-ion batteries due to the abundance of metals like sodium and potassium, in addition to the higher intrinsic safety of aqueous systems. The nanocomposite films (HCFFe/NTC, HCFFe/rGO, HCFBi/NTC, and HCFBi/rGO) were prepared using the liquid-liquid interfacial synthesis method. This method allowed the attainment of integral structures, albeit with an irregular compositional distribution, at the toluene-water interface, facilitating their subsequent transfer onto ITO substrates. The materials were structurally and morphologically characterized by Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The analyses confirmed the formation of HCFFe nanoparticles and HCFBi microparticles distributed within the carbon matrices, and an unprecedented diamond-shaped morphology was observed for HCFBi. The electrochemical performance of the films was optimized through a 23 factorial design, evaluating the influence of the cation type (Na+ or K+), pH, and electrolyte concentration. Cyclic voltammetry results, combined with Dunn’s method, indicated that the HCFFe/rGO film exhibited a predominantly faradaic behavior associated with ion intercalation, whereas the HCFBi/rGO film showed more pronounced capacitive and pseudocapacitive contributions. In galvanostatic charge-discharge tests, the HCFFe/rGO composite reached a specific capacity of 160 mA h g-1, while HCFBi/NTC, despite presenting a lower specific capacity (35.85 mA h g-1), demonstrated remarkable cycling stability after 300 cycles. Additionally, the HCFBi/rGO film presented a specific capacitance of 113.30 F g-1, highlighting its potential for capacitor applications. Fri, 27 Feb 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49008 2026-02-27T00:00:00Z https://repositorio.ufu.br/handle/123456789/49006 Title: Integração de sensores de cor e construção de dispositivos analíticos para medidas em solução e em papel Abstract: This work describes the development and application of analytical devices based on the integration of digital multispectral color sensors (TCS34721, AS7262, AS7341, AS7343, and AS7265x) with microcontrollers, aiming at the construction of intelligent platforms for analytical measurements by reflectance in aqueous solutions and in paper-based analytical devices. Initially, a comparative study was carried out among the TCS34721, AS7262, and AS7341 sensors for the quantification of dyes in aqueous solution. The dyes tartrazine, indigo carmine, ponceau 4R, and sunset yellow were selected because they cover a wide range of the visible spectrum, allowing the evaluation of analytical performance across different spectral regions. The results demonstrated that the AS7341 exhibited superior spectral performance due to its higher multichannel resolution, enabling linear calibration curves, low limits of detection (1 µmol L⁻¹), and adequate precision (RSD = 1.0%). The results obtained with this sensor were comparable to those from a commercial spectrophotometer. Based on these findings, a procedure was developed for the determination of sunset yellow in isotonic beverages, juices, and gelatin, yielding results in agreement with UV–Vis spectrophotometry. Subsequently, the Smart-Sense device was developed, a portable embedded system integrating the AS7341 sensor, electronic control, and a smartphone-based graphical interface, which was successfully applied to the determination of ammonium, iron(II), and nitrite. This system exhibited performance compatible with spectrophotometric methods, in addition to advantages related to portability, low cost, analytical speed, and connectivity. Additionally, the Smart-PAD platform was proposed, consisting of a mechanized system for the reading of paper-based analytical devices. Parameters such as drying time, gain, and integration time were evaluated, with temporal control being critical due to the slow kinetics of the modified Berthelot reaction and the degradation of the reaction product on paper. The platform performs measurements within 8.2 minutes for 18 spots, minimizing the effects of substrate heterogeneity. Its application to ammonium determination showed good linearity (R = 0.997), an RSD of 2.7%, and a detection limit of 6 mg L⁻¹. Overall, the developed devices demonstrate the potential of integrating multispectral sensors with embedded systems as a viable and accessible alternative for chemical analyses, contributing to the democratization of analytical instrumentation and to the advancement of the Internet of Analytical Things (IoAT). Mon, 23 Feb 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49006 2026-02-23T00:00:00Z https://repositorio.ufu.br/handle/123456789/48800 Title: Prospecção química e avaliação do potencial antimicrobiano e antidiabético de espécies dos gêneros Cassia e Senna (Fabaceae) por CLUE-ESI-EM/EM Abstract: The Cerrado and the Atlantic Forest are Brazilian biomes rich in biodiversity, harboring a variety of medicinal plant species. Among them, species of Cassia and Senna have stood out for their medicinal properties and have aroused scientific interest due to the presence of special metabolites with biological potential. In this study, six species of these genera were collected (C. fistula, C. grandis, C. javanica, S. multijuga, S. rugosa, and S. velutina), and nine leaf and flower extracts were prepared and subjected to liquid-liquid extraction to obtain the organic fractions. The obtained extracts were analyzed by UPLC- IES-MS/MS, in negative and positive modes. In this process, flavonoids, an anthraquinone, and proanthocyanidins, along with other classes of compounds, were identified. In the antibacterial activity assay, using cariogenic bacteria, the EE demonstrated moderate activity, with minimum inhibitory concentration (MIC) values ranging from 100 to 400 μg mL–1, the exception being the EE from S. velutina leaves, which exhibited an MIC of 25 μg mL–1 for Streptococcus mitis and 50 μg mL–1 for Porphyromonas gingivalis. In the assay using anaerobic bacteria, the ethyl acetate fraction of S. velutina flowers exhibited a MIC of 50 μg mL–1 against S. mitis. In the assay using aerobic bacteria, the hexane fractions of S. rugosa (flowers) and C. javanica (leaves and flowers) showed antibacterial activity with MIC values ranging from 6.25 to 25 μg mL–1 against P. gingivalis and Actinomyces naeslundii. In the assay to evaluate antifungal activity using yeasts of the genus Candida, the most promising EE were those of S. rugosa and C. javanica flowers, as well as S. velutina leaves and flowers, exhibiting MIC values between 5.86 and 11.72 μg mL–1 against C. glabrata. The most polar fractions of S. rugosa leaves and flowers and C. javanica flowers showed MICs between 2.93 and 23.4 μg mL–1 against C. albicans and C. glabrata. A very promising result was obtained from the ethyl acetate fraction of S. velutina flowers, exhibiting an MIC of 1.46 μg mL–1 against C. glabrata. This fraction was selected for chemical study based on analysis by UPLC-ESI-MS/MS, which revealed the presence of proanthocyanidins, from which the compounds (ent)-cassiaflavan-gallocatechin (A), (ent)-cassiaflavan-(ent)-cassiaflavan- catechin (D), and a mixture of (ent)-cassiaflavan-(4→8)-(epi)-catechin B and C were isolated. The anti-Candida potential of these compounds was evaluated against strains of C. albicans, C. glabrata, and C. tropicalis, and they showed selectivity against C. glabrata with MICs between 1.95 and 15.69 μg mL–1. C. javanica, a species used in folk medicine for the treatment of diabetes, was selected for chemical and antidiabetic study. The dichloromethane fraction of C. javanica flowers was one of the most active in the enzymatic assay against α-amylase and α-glucosidase, and in anti-glycation assays. Chemical analysis of this fraction isolated kaempferol (E), rhein (F), elegentin (G), and afzelin (H), which were also subjected to α-glucosidase and anti-glycation assays. Compound E was one of the most active, particularly in inhibiting α-amylase with an IC50 of 0.04 ± 0.003 μg mL⁻¹ (positive control triticum, 0.2 ± 0.00 μg mL⁻¹). The results of the biological assays highlight the relevance of chemical and pharmacological investigation of Cassia and Senna species, which are still underexplored when it comes to investigating natural products with antimicrobial and antidiabetic potential. Thu, 27 Nov 2025 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48800 2025-11-27T00:00:00Z https://repositorio.ufu.br/handle/123456789/48718 Title: Influência da co-dopagem com íons La3+ em sistemas binários de óxidos de SiO2-TiO2:Eu3+ obtidos pelo método sol-gel Abstract: This study investigates the synthesis and characterization of photoluminescent materials based on SiO2-TiO2 matrices co-doped with Eu3+ and La3+. Prepared via the sol-gel method and calcined at 750 °C, the matrices were analyzed by X-ray Diffraction (XRD), Raman spectroscopy, Fourier-Transform Infrared spectroscopy (FTIR), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and Photoluminescence (PL). Structural results confirmed the stabilization of the anatase phase, where the incorporation of La3+ acted as a crystal growth inhibitor, except at concentrations of 0.3 and 1.0 mol%, which exhibited a singular bulk-like behavior regime. Diffuse reflectance analysis (DRS) revealed an adjustable direct band gap between 2.75 and 3.02 eV, correlated with the structural disorder monitored by the Urbach energy. Thermal treatment proved crucial, promoting the removal of hydroxyl suppressors and resulting in an average 6.5-fold (547%) jump in luminescence lifetimes (τ), which reached values exceeding 1000 µs. Spectroscopic analysis indicated that La3+ co-doping induces a symmetry breaking at the Eu3+ local site (site symmetries Cs, Cn ou Cnv), evidenced by the splitting of the 5D0→7F1 transition into three singlets and a 120% increase in the emission intensity of the 5D0→7F2 hypersensitive band. In situ PL monitoring as a function of temperature confirmed the reversibility and thermal robustness of the system, mitigating quenching effects. These findings demonstrate the high potential of SiO2-TiO2:Eu3+,La3+ composites for the development of advanced photonic devices, such as WLEDs and high-sensitivity sensors for optical thermometry. Wed, 17 Dec 2025 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48718 2025-12-17T00:00:00Z